Technological Field
The present invention relates to a biological information detector, a biological information measuring device, and method for designing a reflecting part in the biological information detector and the like.
Background Technology
A biological information measuring device measures human biological information such as, for example, pulse rate, blood oxygen saturation level, body temperature, or heart rate, and an example of a biological information measuring device is a pulse rate monitor for measuring the pulse rate. Also, a biological information measuring device such as a pulse rate monitor may be installed in a clock, a mobile phone, a pager, a PC, or another electrical device, or may be combined with the electrical device. The biological information measuring device has a biological information detector for detecting biological information, and the biological information detector includes a light-emitting part for emitting light towards a detection site (e.g., finger or arm) of a test subject (e.g., a user), and a light-receiving part for receiving light having biological information from the detection site.
There is disclosed in Japanese Laid-Open Publication No. 2004-337605 a reflection-type light sensor in which a light-emitting element and a light-receiving element are coaxially provided. The reflection-type light sensor described in Japanese Laid-Open Publication No. 2004-337605 is designed so that the detection sensitivity of the light-receiving element is at a maximum when a detection target (e.g., a finger) is positioned at a predetermined distance away from a window for transmitting light emitted from the light-emitting element. In paragraph [0032] in Japanese Laid-Open Publication No. 2004-337605, it is disclosed that the emission angle of the light-emitting element can be changed, the size of a substrate can be changed, and the curvature or focal point of a reflecting surface can be changed, in order to set a peak position at which the detection accuracy is at a maximum.
Light emitted by the light-emitting element illuminates a detection site of a test subject via a light-transmitting member (corresponding to a window part in Japanese Laid-Open Publication No. 2004-337605). A part of the light emitted by the light-emitting element is reflected on a surface (and a vicinity of the surface) of the light-transmitting member. The reflected light is light that has been reflected directly on the surface (and a vicinity of the surface) of the light-transmitting member (i.e., directly reflected light), and directly reflected light is invalid light that does not have biological information (i.e., noise light). In an instance in which the directly reflected light (i.e., invalid light) is incident on a light-receiving region of the light-receiving element, the S/N (i.e., signal-to-noise ratio) of a biological information detection signal outputted from the light-receiving element decreases. In order to improve the measurement sensitivity of a biological information measuring device, it is important to design a light-collecting optical system (i.e., a reflecting part) so as to minimize incidence of directly reflected light (i.e., invalid light) on the light-receiving region of the light-receiving element. Merely adjusting the focal length of the reflecting surface as with Patent Citation 1, for example, does not remove the effect of reflected light that has been reflected on a surface side of the light-transmitting member (i.e., the window part), i.e., the effect of directly reflected light (e.g., a decrease in the S/N of the detection signal outputted from the light-receiving element).